1. Department of Physiology
The Urinary System
Dr. Ahmed Al-Dwairi
Department of Physiology

2. Functions of the Urinary System
Contributing to homeostasis
Controlling electrolyte and water balance of the ECF, plus urinary output.
If the ECF has an excess of water or electrolytes, the kidneys eliminate the excess. If there is a deficiency of these substances, the kidneys can reduce the loss of these from the body.
Maintaining the proper osmolarity of body fluids
Maintaining proper plasma volume
Helping to maintain proper acid-base balance
Excreting wastes of body metabolism
Excreting many foreign compounds
Producing erythropoietin and renin
Converting vitamin D to an active form
Gluconeogenesis
Secretion of prostaglandin

3. Excretion of Metabolic Waste Products
Urea (from protein metabolism)
Uric acid (from nucleic acid metabolism)
Creatinine (from muscle metabolism)

4. Secretion, Metabolism, and Excretion of Hormones
Hormones produced in the kidney
Renal erythropoetic factor
1,25 dihydroxycholecalciferol (Vitamin D)
Renin
Hormones metabolized and excreted by the kidney
Most peptide hormones (e.g. insulin, angiotensin II, etc.)

5. Body fluid regulation
Guyton and Hall, Medical physiology 11th edition.

7. Anuria = less than 100 cc per day
Appearance
Clear = normal
Cloudy = ? Infection
If sediment = kidney disease
Dark = ?blood, ?bilirubin, ?concentrated
Color
Urochrome pigment = yellow
comes from breakdown of hemoglobin
Concentration
More Concentrated = Deeper Yellow
Change of Color From:
Meds
Vitamin = yellow
Diseases
Blood = red-brown
Liver = Orange
Foods
Rhubarb = red-brown
Odor
Normal = ammonia-like smell
from breakdown of urea
Unpleasant = ? infection
Quantity
Average per 24 hours = 1500 cc
60 cc per hour
GFR = 125 cc/min
Thus, cc/ hour
Urine Made Per Hour = 60 cc
GFR, Per Hour = cc
KEY: 1 % of filtered urine remains urine; 99 % becomes reabsorbed back into blood
Oliguria = cc per day
Anuria = less than 100 cc per day
Polyuria = diabetes, nerves, diuretics

8. Protein Specific Gravity Glucose pH Ketone
OK to have a Trace in the urine
Benign Conditions:
exercise
exposure to cold
 protein consumption
Generally Means Kidney Disease
Glucose
Will only be in urine if exceed Renal Threshold.
Ketone
Ketones are products of Fat Metabolism
If cant breakdown Sugars for energy, the body will begin using Fat
Seen in:
Uncontrolled Diabetes
Starvation
Hi-Fat Diet
Specific Gravity
Determines Concentration
Compares Test Liquid to H2O
Normal =
In many kidney diseases, one loses the ability to concentrate urine pH
Determines Acidity or Alkalinity
Normal = 6.0
Range =
Acidity example = diabetes
Alkaline example = UTI

9. Physiological Anatomy
Kidneys
– The functional units of the system
Ureters
Urinary Bladder
Conducting & Storage components
Urethra

10. Physiological anatomy:
1. General organization :
150 gm, size of a clenched fist.
Consists of capsule, outer cortex, and inner medulla.
Medulla (renal pyramids)  papilla  renal pelvis  ureter  bladder  urethra

11. 2. Renal blood supply : 22% C.O  1100 ml/min .
Renal artery  interlobar arteries  arcuate arteries  interlobular arteries  afferent arterioles  glomerular capillaries  efferent arterioles  peritubular capillaries  venous system .

12. Physiologic Anatomy
Each kidney is supplied by a renal artery and renal vein. The kidney acts on the blood plasma flowing through it.
As urine is formed, it drains into the renal pelvis and is channeled into the ureter.
The urine is stored in the urinary bladder. It is emptied periodically through the urethra.
The urethra serves the urinary and reproductive tracts in the male.

13. Guyton and Hall, Medical physiology 11th edition.

14. The nephron; the functional unit of the kidney
Nephron is the smallest unit that can perform all the functions of the kidney. Each kidney has about one million nephrons.
Kidney layers:
Cortex: the outer layer, looks glomerular.
Medulla: the inner layer made up of striated triangles; the renal pyramids.
The nephrons are arranged through the cortex and medulla of the kidney.
Each nephron consists of:
Vascular component
Tubular component.

15. The vascular component; the dominant portion of the nephron

16. The tubular component; a hollow tube with different regions
Renal corpuscle – the glomerulus and its Bowman’s capsule

17. Juxtaglomerular Apparatus
Combined vascular/tubular microscopic structure in the kidney regulating the function of each nephron
Between the vascular pole of the renal arterioles and the returning distal convoluted tubule of the same nephron
Cellular components of the apparatus:
Macula densa of the distal convoluted tubule,
Senses any increase in sodium chloride concentration in the distal tubule of the kidney and secretes a locally active (paracrine) vasopressor which acts on the adjacent afferent arteriole
Smooth muscle cells of the afferent arteriole
Juxtaglomerular cells (granular cells), Secrete renin

18. Types of Nephrons Cortical nephron Juxtamedullary nephron
Glomeruli in outer cortex & short loops of Henle that extend only short distance into medulla
Majority of nephrons
Cortical interstitial fluid 300 mOsmolar
Juxtamedullary nephron
Glomeruli in inner part of cortex & long loops of Henle which extend deeply into medulla
Blood flow through vasa recta in medulla is slow
This nephron maintains osmolality in addition to filtering blood and maintaining acid-base balance

19. Basic Processes of the Nephron
Glomerular filtration is the first process. A protein-free plasma is filtered from the glomerulus into the Bowman’s capsule. Blood cells are not normally filtered. Normally about 20 % of the plasma is filtered. Glomerular filtrate is produced at the rate of 125 ml per minute (180 liters per day).
The 80% of the plasma not filtered passes into the efferent arteriole and through the peritubular capillaries.
Tubular reabsorption, filtered substances move from the inside of the tubular part of the nephron into the blood of the peritubular capillaries. The reabsorption rates of most substances are very high. (of the 180 liters filtered, liters are reabsorbed)
Tubular secretion is a selective process by which substances from the peritubular capillaries enter the lumen of the nephron tubule.
Urine excretion results from these three processes
= GF – TR + TS

20. Renal Handling of
Different Substances
Figure 26-10

21. Glomerular Filtration

22. Renal Handling of Water and Solutes
Filtration Reabsorption Excretion
Water
(liters/day) 1
Sodium 25, ,410
(mmol/day)
150
Glucose
(gm/day)
Creatinine
(gm/day)

23. Glomerular Filtration
GFR = 125 ml/min = 180 liters/day
Plasma volume is filtered 60 times per day
Glomerular filtrate composition is about the
same as plasma, except for large proteins
Filtration fraction (GFR/Renal Plasma Flow)
= 0.2 (i.e., 20% of plasma is filtered)

24. Nephron Filtration Membrane
1. The wall of the glomerular capillaries, which is a single
layer of flattened endothelial cells. It is perforated by many
large pores that make it over 100 times more permeable to H2O
and solutes than capillaries elsewhere in the body.
2. The basement membrane, which is an acellular (lacking
cells) gelatinous layer.
3. The inner layer of Bowman’s capsule, which consists of
podocytes, octopus-like cells that encircle the glomerular tuft.

25. The filtration membrane
Guyton and Hall, Medical physiology 11th edition.

26. Why huge GFR? 1) Most waste product are removed rapidly
2) Allow all body fluids to be filtered and processed by kidneys many times each day .
 60 times/day
 high GFR provides precise & rapid control over body fluids (volume, composition)

27. Effects of size and electrical charge of dextran on filterability by glomerular capillaries.
Figure 26-12

28. Glomerular Filtration Forces
No active transport mechanisms or local energy expenditure are involved in in moving fluid across the glomerular membrane into Bowman’s capsule.
Passive physical forces, with the same principles of fluid dynamics are involved in filtration:
The glomerular capillary hydrostatic pressure is the result of the blood pressure pushing on the inside of the capillary wall (e.g., 60 mm Hg).
It is the major force that induces glomerular filtration. Depends contraction of the heart, and afferent/efferent arteriolar resistance.
The plasma-colloid osmotic pressure is due to the retention of plasma proteins in the blood of the glomerulus.
The concentration of water is higher in the glomerulus. Water tends to return to the blood in the glomerulus by osmosis (32 mm Hg).
The capsule hydrostatic pressure tending to move fluid from the Bowman’s capsule into the glomerulus (18 mm Hg).

29. Net filtration pressure
 PG – PB – VTG + VTB
 60 – 18 – = 10 mmHg
K= 12.5 ml/min/mmHg

30. Glomerular Filtration Rate (GFR)
Glomerular Filtration Rate (GFR): the total amount of filtrate formed per minute by the kidneys
GFR regulation is mainly due to changes in the glomerular capillary blood pressure; a higher arterial blood pressure supplying the glomerulus can increase the GFR.

31. Factors that affect GFR
1. ↓ Glomerular capillary filtration coefficient ↓ GFR
e.g.: chronic uncontrolled hypertension, DM
2. ↑ Bowman's capsule hydrostatic pressure ↓ GFR
e.g.: stones

32. Glomerular Capillary Filtration Coefficient (Kf)
Kf = hydraulic conductivity x
surface area
Normally it is not highly variable
Disease that can reduce Kf and GFR
- chronic hypertension
- obesity/diabetes mellitus
- glomerulonephritis

33. 3. ↑ Glomerular capillary colloid osmotic pressure ↓ GFR:
Averages 32 mmHg and this pressure is determined by:
Arterial plasma colloid osmotic pressure
Fraction of plasma filtered (filtration Fraction)
 increased by: ↑GFR or ↓renal plasma flow

34. 4. ↑ Glomerular capillary hydrostatic pressure  ↑ GFR :
Important in physiological regulation of GFR
this pressure is determined by:
Arterial pressure
Afferent arteriolar resistance
Efferent arteriolar resistance this has biphasic effect:
Moderate ↑resistance  slight ↑ GFR
Severe constriction ↓ GFR

35. Effect of change in afferent arteriolar resistance or efferent arteriolar resistance on glomerular filtration rate and renal blood flow.

37. Regulation of GFR and renal blood flow
Changes in the GFR primarily result from changes in glomerular capillary blood pressure. Changes in plasma colloid osmotic pressure and Bowman’s capsule hydrostatic pressure are not subject to regulation and do not vary much under normal conditions.
Uncontrolled shifts in the GFR can lead to fluid and electrolyte imbalances.
Three basic mechanisms to keep relatively constant GFR despite changing mean arterial pressure
Autoregulation
Tubuloglomerular feedback mechanism
ANS and Hormones.

39. Renal blood flow control
Autoregulation of GFR and Renal blood flow :
GFR remains constant if the Arterial pressure ranges from 75 to 160 mmHg.
Normally filtration= 180 /day, reabs.= 178.5/day  urine=1.5 /day
Without autoregulation if pressure ↑ by 25%  GFR = 225 L/day If reabsorption is constant urine= 46.5 L/day.
30 folds increase in urine formation depletes the body

40. Renal blood flow:
1100 ml/min 22% c.o
large fraction of O2 is consumed by the kidneys due to the high rate of active sodium reabsorption by the tubules

41. Regulation of GFR
Autoregulation; myogenic, altering the caliber of the afferent arterioles due to stretch.
If the GFR rises by increased arterial pressure, the afferent arterioles constrict. This lowers the GFR.
If the GFR decreases, the afferent arterioles dilate. This increases the GFR.

42. Renal blood flow control (cont.)
Sympathetic N.S :
Strong activation↓GFR and flow
Moderate activation little effect
Sympathetic nervous system plays an important role on adjusting glomerular blood flow, while parasympathetic nervous system does not have any influence on the kidneys.
Sympathetic innervation to afferent arterioles,  vasoconstriction
Stimulated when blood pressure drops to reduce GFR and conserve fluid volume.
Stimulation of sympathetic nerves increases the release of renin by the kidneys

43. Renal blood flow control(cont.)
Hormones and autacoids:
Norepinephrine , epinephrine, endothelin constrict renal blood vessels and decreases GFR
Angiotensin II constricts efferent arterioles ↑GFR - ↑ Na, H2O reabsorption.
Endothelial - Derived Nitric oxide decreases resistance and ↑ GFR
Prostaglandins, bradykinin cause vasodilatation

44. Regulation of GFR Tubuloglomerular feedback mechanism.
sensing changes in flow in the nephron’s tubular component.
The cells of the macula densa monitor NaCl concentration in the fluid moving into the distal convoluted tubule.
If GFR increases, then NaCl movement also increases
Macula densa cells send a paracrine message causing the afferent arteriole to contract, decreasing GFR and NaCl movement

45. Autoregulation and glomerulotubular balance try to maintain a constant GFR
 these processes are not 100% effective so ↑BP will always lead to ↑GFR (pr. Diuresis or pr. Natriuresis) .

46. Baroreceptor reflex influence on the GFR in long-term regulation of
arterial blood pressure